Meeting Abstract

54.5  Tuesday, Jan. 5  Multiple roles of retinoic acid in the pharyngeal endoderm development of amphioxus KOOP, D.*; HOLLAND, L.Z.; Univ. of California, San Diego; Univ. of California, San Diego dkoop@ucsd.edu

In the cephalochordate, amphioxus, the pharyngeal endoderm gives rise to Hatschek’s pit (homologous to the vertebrate adenohypophysis), endostyle (homologous to the vertebrate thyroid) and gills. However, in vertebrates, pharyngeal structures receive a major contribution from neural crest cells, whereas amphioxus lacks neural crest facilitating the study of the role of the endoderm in pharyngeal patterning. In both amphioxus and vertebrates homologous suites of genes pattern the pharyngeal endoderm. These include Tbx1/10, Eyes absent, Six genes and Pax genes. Our previous studies have demonstrated that retinoic acid (RA) signalling, mediated by Hox established the posterior limit of the pharyngeal endoderm. Here we present a second role for RA signalling in the development of the gills. To investigate the role of RA signalling during pharyngeal endoderm morphogenesis, we examined the effects of late RA treatments on the genes that pattern the gill pimordia such as Six and Pax genes. Our results show that at later stages in development RA does not inhibit gill primordia formation but does plays an important role in regulating gene expression and apoptosis in the forming gill slits. These results suggest that in amphioxus, as in vertebrates, pharyngeal development involves a complex interaction of signalling pathways, often playing multiple roles.